Messages in this thread | | | Date | Thu, 15 Feb 2024 21:40:40 +0100 | Subject | Re: [PATCH 1/2] wordpart.h: Helpers for making u16/u32/u64 values | From | Michal Wajdeczko <> |
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On 14.02.2024 23:09, Kees Cook wrote: > On Wed, Feb 14, 2024 at 10:46:53PM +0100, Michal Wajdeczko wrote: >> It is quite common practice to make u16, u32 or u64 values from >> smaller words. Add simple helpers for that. >> >> Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com> >> --- >> v2: new macro names due to conflict with crypto/aria.h >> explicit cast and truncation everywhere (Alexey) >> moved to wordpart.h (Andy) >> --- >> Cc: Kees Cook <keescook@chromium.org> >> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> >> Cc: Alexey Dobriyan <adobriyan@gmail.com> >> Cc: Jani Nikula <jani.nikula@intel.com> >> --- >> include/linux/wordpart.h | 32 ++++++++++++++++++++++++++++++++ >> 1 file changed, 32 insertions(+) >> >> diff --git a/include/linux/wordpart.h b/include/linux/wordpart.h >> index f6f8f83b15b0..8c75a5355112 100644 >> --- a/include/linux/wordpart.h >> +++ b/include/linux/wordpart.h >> @@ -31,6 +31,38 @@ >> */ >> #define lower_16_bits(n) ((u16)((n) & 0xffff)) >> >> +/** >> + * make_u16_from_u8 - make u16 value from two u8 values >> + * @hi: value representing upper 8 bits >> + * @lo: value representing lower 8 bits >> + */ >> +#define make_u16_from_u8(hi, lo) ((u16)((u16)(u8)(hi) << 8 | (u8)(lo))) > > Do we want to actually do type validation here? Right now it's just > cast/truncating, which based on the version log is by design. Is silent > truncation the right thing to do?
note that even FIELD_PREP() is doing silent truncation and these macros here could be treated as specialized/simplified variants of FIELD_PREP() as alternate implementation can look like:
#define make_u16_from_u8(hi, lo) \ ((u16)(FIELD_PREP_CONST(GENMASK(15, 8), (hi)) | \ FIELD_PREP_CONST(GENMASK(7, 0), (lo))))
#define make_u32_from_u16(hi, lo) \ ((u32)(FIELD_PREP_CONST(GENMASK(31, 16), (hi)) | \ FIELD_PREP_CONST(GENMASK(15, 0), (lo))))
#define make_u64_from_u32(hi, lo) \ ((u64)(FIELD_PREP_CONST(GENMASK_ULL(63, 32), (hi)) | \ FIELD_PREP_CONST(GENMASK_ULL(31, 0), (lo))))
but then it will not match simplicity of the lower|upper_XX_bits macros
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